1. Field of the Invention
The present invention relates generally to graphics generated on a computer. More particularly, the present-invention relates to modification of existing computer line graphics. Specifically, the present invention relates to an apparatus and method for modifying computer generated vector graphics to have a more humanistic appearance by varying the line widths of the vector graphics.
2. Description of Related Art
Computer graphics can be divided into two broad categories, raster and vector. These categories differ primarily in the manner that drawing data is created, stored, and edited. Raster graphics, often called bitmaps, are two dimensional arrays of picture elements. Similar to grains in a photograph, each picture element (pixel) has a color value. The collection of these pixels and their corresponding values form a raster image.
In contrast, vector graphics are based on a definition of geometric shapes. Shapes are defined by precise mathematically defined Cartesian points. Thus, the shapes may be lines, rectangles, curves, or any arbitrary polygon defined by mathematical points. The collection of these geometric shapes and their mathematical definitions form a computer vector drawing.
Shapes in a vector drawing are divided up into strokes and fills. Strokes indicate that a vector shape should be drawn with a constant width of pixels of some color value. Fills indicate that the boundary of a shape should be closed and the interior filled with pixels of some color value. Strokes and fills that share the same shape differ in the method by which a shape is rendered.
A long-standing goal in computer graphics has been to enable computer users to produce output that does not look computer generated. The very strength of computer graphics, that is, the exact definition of an image or drawing, has been a liability because humans do not draw with such perfection. Consequently, most graphics generated on a computer look artificial.
When using raster graphics, the problem of the artificial appearance of drawings can be corrected somewhat by using digital filters. The color value of each pixel within a raster image is modified algorithmically by a digital filter. The filtering algorithms, originally based on photographic image processing, can get very complex and can provide interesting "painting" effects. Raster digital filters can modify raster images and create such appearances as watercolor or oil painting.
Unfortunately, the effects available to raster graphics do not apply to vector graphics. The analogy again is the difference between photographs and mathematical graphs. A computer user working with the desirable preciseness of vectors graphics must forfeit the pleasure of automatically producing a vector that could appear hand drawn.
Therefore, there is a strong desire for a system that would enable a computer draftsman to benefit from the preciseness offered by vector graphics, but also be able to simply and easily produce more humanistic appearing drawings.